Many traditional user-interfaces, human-computer interfaces, and the like, are cold, mechanical/tegical and lack an expressive continuous “fluid” and immersive form of interaction.
Some user-interfaces, such as proximity-based, or antenna-based musical instruments like the Theremin, or “Doppler Danse” (Steve Mann “Doppler Danse”, Leonardo, Vol. 25, Iss. 1, 1992), achieve the desirable more continuous and immersive form of interaction but lack tactile feedback.
Likewise, “air typing” keyboards suffer from similar problems, as do many of the vision-based systems such as David Rokeby's “Very Nervous System” (a vision-based system that uses a camera as an input device to control virtual musical instruments, by tracking people's body position in space).
Playing these instruments is very difficult because they provide no “feel” of where individual notes are located.